Method and arrangement for positioning a wireless device

ABSTRACT

A method in a network node and a network node with positioning functionality in a wireless communications network in a multi-carrier system are described. The network node enables positioning measurements for a wireless device in the multi-carrier system based on at least one capability indicator that identifies on which carrier frequencies positioning measurements in the multi-carrier system can be performed.

PRIORITY APPLICATIONS

This application is a continuation application claiming priority fromU.S. application Ser. No. 13/393,322, filed Feb. 29, 2012, which is theU.S. national phase of International Application No. PCT/SE 2012/050158,filed Feb. 15, 2012, which designated the U.S. and which claims priorityfrom U.S. Provisional Application No. 61/444,235, filed Feb. 18, 2011,the entire contents of each of which are hereby incorporated byreference.

TECHNICAL FIELD

The present technology described relates to a method in a network nodewith positioning functionality in a wireless communications network in amulti-carrier system to enable UTDOA, Uplink Time Difference of Arrival,positioning measurements for a wireless device in the multi-carriersystem, and the network node with positioning functionality in thewireless communications network in the multi-carrier system to enableUTDOA, Uplink Time Difference of Arrival, positioning measurements forthe wireless device in the multi-carrier system.

BACKGROUND

To enhance peak-rates within a cellular technology, multi-carrier orcarrier aggregation solutions are known to be efficient. Each carrier inmulti-carrier or carrier aggregation system is generally termed as acomponent carrier (CC) or sometimes is also referred to a cell. The termcarrier aggregation (CA) is also called (e.g. interchangeably called)“multi-carrier system”, “multi-cell operation”, “multi-carrieroperation”, “multi-carrier”, “multi-frequency carrier” transmissionand/or reception. This means that the CA is used for transmission ofsignaling and data in the uplink and/or downlink directions. One of theCCs is the primary carrier or anchor carrier and the remaining ones arecalled secondary or supplementary carriers. Generally the primary oranchor CC carries the essential UE specific signaling. The primary CCexists in both uplink and direction CA. The network may assign differentprimary carriers to different UEs operating in the same sector or cell.Further, carriers may be activated or deactivated for different UEs.Thanks to carrier aggregation, the UE has more than one serving cell:one primary serving cell and one or more secondary serving cell. Theserving cell is interchangeably called as primary cell (PCell) orprimary serving cell (PSC) or serving cell on primary CC. Similarly thesecondary serving cell is interchangeably called as secondary cell(SCell) or secondary serving cell (SSC) or serving cell on secondary CC.Regardless of the terminology, the PCell and SCell(s) enable the UE toreceive and transmit data. More specifically the PCell and SCell existin DL and UL for the reception and transmission of data by the UE. Theremaining non-serving cells on the PCC and SCC are called neighborcells. The CCs belonging to the CA may belong to the same frequency band(aka intra-band CA) or to different frequency band (inter-band CA) orany combination thereof (e.g. 2 CCs in band A and 1 CC in band B). Thecarriers in intra-band CA can be adjacent (aka contiguous) ornon-adjacent (aka non-contiguous).

Dual-Carrier High-Speed Downlink Packet Access (DC-HSDPA, also known asDual-Cell HSDPA) was introduced within the 3rd Generation PartnershipProject (3GPP) Rel-8. DC-HSDPA enables reception of data from two cellssimultaneously, transmitted on two adjacent carriers in a same basestation and sector, to individual wireless devices. The concept ofDC-HSDPA is in 3GPP Rel-10, being extended e.g. to 4 downlink carriers(known as 4C-HSDPA).

In HSPA release 10 up to 4 downlink carriers can be aggregated as4C-HSDPA where the downlink carriers or cells may belong to the samefrequency band or may be split over two different frequency bands e.g. 3adjacent downlink carriers in band I (2.1 GHz) and 1 downlink carrier inband VIII (900 MHz). In HSPA Rel-11 even up to 8 downlink carriers maybe aggregated, this configuration may be denoted as 8C-HSDPA; thedownlink carriers may be distributed over 2 or even more bands.

To complement DC-HSDPA, in 3GPP Rel-9, Dual-Carrier High-Speed UplinkPacket Access (DC-HSUPA) was also introduced. DC-HSUPA enables anindividual wireless device to transmit data on two adjacent carrierssimultaneously to a radio access network. DC-HSUPA according to 3GPPRel-9 is in essence an aggregation of legacy (Rel-8, single-carrier)HSUPA.

In LTE (Long Term Evolution) intra-band CA up to 5 downlink carriers and5 uplink carriers each of up to 20 MHz may be aggregated by the wirelessdevice. In LTE inter-band CA, up to 5 downlink and 5 uplink carrierseach of up to 20 MHz and belonging to different bands can be aggregatedby the wireless device. Even additional carriers may be introduced infuture releases. CC in CA may or may not be co-located in the same siteor base station. For instance the CCs may originate (i.e.transmitted/received) at different locations (e.g. from non-collocatedBSs (Base Stations), RRHs (Radio Remote Head) or RRUs (Radio RemoteUnit).

Although the additional spectrum bandwidth associated with multi-carrieroperation does not increase “spectral efficiency” (maximum achievablethroughput per cell per Hz [bps/cell/H]), the experienced user datarates are increased significantly. In particular, for bursty packet datatraffic at low and moderate load, the data rate is proportional to thenumber of carriers exploited. Moreover, power inefficient higher ordermodulation schemes can be avoided (which is especially important in theuplink) and the practical as well as theoretical peak data rate of thesystem are naturally increased.

In a network according to the 3GPP specifications a RNC (Radio NetworkController) controls radio resources and radio connectivity within a setof cells. Handover and radio access bearer admission control is presumedto be conducted in the RNC based on measurements of path loss etc on aprimary carrier (alternatively referred to as an anchor carrier). RAN(Radio Access Network) is according to the 3GPP specificationresponsible for the radio transmission and control of the radioconnection. A Node-B, also referred to as Node B, handles the radiotransmission and reception within one or more cells. In case of adistributed RAN architecture where Node-B and RNC functionality asdefined in 3GPP specifications are co-located in the base station, thebase station would naturally handle also these functionalities. In aDC-HSUPA capable Node-B, the other carrier, which is referred to as asecondary carrier, is assumed to be configured by the RNC for a givenDC-HSUPA capable wireless device and then scheduled and activated by theNode-B whenever feasible and useful (with the standard objectivefunction to maximize the supported traffic volumes, or aggregate systemthroughput, subject to fairness criteria and quality of serviceconstraints, such as minimum bit rate or maximum latency requirements).A primary carrier, on the other hand, may not be temporarily deactivatedby the Node-B: to deactivate a certain primary carrier for a connection,the connection is either released, or an inter-frequency handover isperformed (in which case another carrier will become the primarycarrier).

For each wireless device connected in DC-HSUPA mode, the serving Node-Bhence controls whether or not a secondary carrier is activated, and aseparate grant is selected for each activated carrier.

Furthermore, if a secondary carrier is activated by the Node-B, it isassumed that the Dedicated Physical Control Channel (DPCCH), whichincludes a sequence of pilot bits, is transmitted in uplink on thatcarrier, and the Node-B hence tries to detect this signal.

UTRAN (Universal Terrestrial Radio Access Network) is a collective termfor the Node B's and RNCs which make up a UMTSRadio Access Network(RAN). The wireless device may be in a CELL_FACH state, where the UTRANmay redirect the wireless device to another frequency. In a futuresystem, one can envisage multi-carrier operations in the CELL_FACHstate. Node-B controlled carrier selection of the uplink transmissionswill then be introduced.

Load estimation in the WCDMA (Wideband Code Division Multiple Access)uplink is performed for many reasons in prior art. Most importantly, thepresent scheduling of enhanced uplink traffic is based on the principleto schedule users until a load threshold is reached. Such schedulingdecisions are taken every 2/10 ms transmission time interval (TTI).Thresholds are typically used in order to maintain a planned coverage,and to maintain cell stability avoiding inner loop power control (ILPC)rushes. When coverage is addressed neighbour cell interference isincorporated in the load measure, this is not the case when cellstability is treated. The scheduling and load estimation functionalityand algorithms are both located in the WCDMA RBS.

It is also possible to use the estimated uplink load in load basedadmission control algorithms. Also this is known in prior art. Thesealgorithms use the uplink load in order to determine if new users can beadmitted in specific cells. The admission control functionality islocated in the RNC node. Signaling means for signaling of load isavailable over an NBAP interface. It is e.g. shown in H. Holma and A.Toskala, WCDMA for UMTS—Radio Access for Third Generation MobileCommunications. Chichester, UK: Wiley, 2000 that without advancedinterference suppressing (IS) receivers and interference cancellation(IC), the load defined at an antenna connector is given by the noiserise, or rise over thermal, RoT(t), defined by

${{{RoT}(t)} = \frac{{RTWP}(t)}{N}},$where N is the thermal noise level as measured at the antenna connector.The definition of RTWP(t) is the total wideband power

${{{RTWP}(t)} = {{\sum\limits_{k = 1}^{K}\;{P_{k}(t)}} + {I(t)} + N}},$also measured at the antenna connector. Here P_(u)(t), u=1, . . . , U,denotes the power of uplink user u, and I(t) denotes the power asreceived from neighbor cells of the WCDMA system. A problem that nowneeds to be addressed is that the signal reference point is, bydefinition, at the antenna connector. The measurements are, however,obtained after an analogue signal conditioning chain, in a digitalreceiver. The analogue signal conditioning chain may unfortunatelyintroduce a scale factor error of about 1-3 dB. Fortunately, all powersof the cell are almost equally affected by the scale factor error sowhen the RoT is calculated, the scale factor error is cancelled as

${{RoT}^{{Digital}\mspace{14mu}{Receiver}}(t)} = {\frac{{RTWP}^{{Digital}\mspace{14mu}{Receiver}}(t)}{N^{{Digital}\mspace{14mu}{Reciever}}(t)} = {\frac{{\gamma(t)}{{RTWP}^{Antenna}(t)}}{{\gamma(t)}{N^{Antenna}(t)}} = {{{RoT}^{Antenna}(t)}.}}}$

The RoT can hence be measured in the receiver. The major difficulty ofany RoT estimation algorithm still remains though, namely to separatethe thermal noise power from the interference from neighbor cells. Thatthis is troublesome can be seen from the following equation, where E[ ]denotes statistical expectation, and where Δ denotes the variationaround the mean.I ^(N)(t)+N(t)=E[I ^(N)(t)]+E[N(t)]+ΔI ^(N)(t)+ΔN(t).

The fundamental problem can now be clearly seen. Since there are nomeasurements available in the RBS that are related to the neighbor cellinterference, a linear filtering operation can at best estimate the sumE[^(N)(t)]+E[N(t)]. This estimate cannot be used to deduce the value ofE[N(t)]. The situation is the same as when the sums of two numbers areavailable. Then there is no way to figure out the values of theindividual numbers. This issue is analyzed rigorously for the RoTestimation problem in T. Wigren, “Soft uplink load estimation in WCDMA”,IEEE Trans Veh. Tech., February, 2009 where it is proved that the noisepower floor is not mathematically observable. Nonlinear algorithms thatprovide approximate estimates of the noise floor are therefore used.

One algorithm that is currently in use estimates the RoT. One mainproblem solved by the estimation algorithm is the accurate estimation ofthe thermal noise floor N. Since it is not possible to obtain exactestimates of this quantity due to the neighbor cell interference, theestimator therefore applies an approximation, by consideration of thesoft minimum as computed over a relative long window in time. It isimportant to understand that this estimation relies on the fact that thenoise floor is constant over very long periods of time (disregarding thesmall temperature drift).

The sliding window algorithm described above has the disadvantage ofrequiring a large amount of storage memory. This becomes particularlytroublesome in case a large number of instances of the algorithm areneeded, as may be the case when IC is introduced in the uplink. Toreduce the memory consumption a recursive algorithm was disclosed in thepatent application T. Wigren, “Method and arrangement formemory-efficient estimation of noise floor”, International PatentApplication, PCT/SE20061050347, 2006. (P22298). That algorithm reducesthe memory requirements of the sliding window scheme discussed above atleast by a factor of 100.

The difference with the interference suppressing G-rake receiver ascompared to a conventional RAKEreceiver is that each user sees a reducedlevel of interference, immediately after the so called weight combiningstep. In G-rake+, a covariance matrix {circumflex over (R)}_(u), u=1, .. . , U, with the order equal to the number of fingers is firstestimated to capture the interference. The codes not used by the presentuser u may be used in order to estimate {circumflex over (R)}_(u).

The GRAKE+ receiver uses the estimated covariance matrix that models theinterference for computation of the combining weights for the users u,u=1, . . . , U.{circumflex over (R)} _(u) ŵ _(u) =ĥ _(u) , u=1, . . . ,Uwhere ĥ_(u), u=1, . . . , U, is the net channel response of user u andwhere ŵ_(u) are the combining weights.

The effect of the above equation is that GRAKE+ essentially whitens thecorrelated interference and removes large spectral peaks frominterferers at certain finger locations and for certain antennaelements.

Note that GRAKE+ is still a linear receiver. There is a related type ofIC receiver for WCDMA which is also linear, denoted the chip equalizer.The difference between GRAKE+ and the chip equalizer is simply the orderof certain basic operations.

The now public patent application T. Wigren, “Load estimation ininterference whitening systems”, PCT/SE2009/051003 discloses means forestimation of the RoT, as seen by a user after G-rake+. This patentapplication defines a new signal after G-rake processing and evaluatesRoT for that signal.

However, the algorithm of T. Wigren, “Load estimation in interferencewhitening systems”, PCT/SE2009/051003 requires inversion of theimpairment matrix of each user and is too computationally demanding tobe preferred presently. The Frequency Domain Pre Equalizing (FDPE)receiver is another interference suppressing receiver. It also affectsthe measurement of uplink load. The main advantages associated with thestructure of this receiver are that the FDPE structure gives significantIS gains and that the FDPE structure achieves IS for all userssimultaneously, thereby reducing the computational complexity ascompared to the G-rake structure that performs processing individuallyfor all users. Processing blocks are inserted in the uplink receiverstructure that is already in place, thereby reducing development cost.The fast Fourier transform (FFT) accelerator hardware developed for LTEcan be reused, thereby creating further synergies for the new DUS HW ofthe RBS.

The FDPE algorithm performs interference whitening in the frequencydomain. To explain this in detail, the following time domain signalmodel can be used

${v(t)} = {{\sum\limits_{l = 0}^{L - 1}\;{{h(l)}{z\left( {t - l} \right)}}} + {{\eta_{v}(t)}.}}$

Here ν is the received (vector due to multiple antennas) signal, withchip sampling rate, h is the radio channel net response, z is thedesired (transmitted) signal, and η_(v) denotes thermal noise andinterference, t denotes discrete time.

Taking the Fourier transform, translates the time domain equation intoV(m)=H(m)Z(m)+N(m)where the quantities are the discrete Fourier transform of thecorresponding time domain quantities.

Now a whitening filter can be applied in the frequency domain. It isknown that the filter that minimizes the mean square error (the MMSEsolution) is given by

${W_{MMSE}(m)} = {{\left( {{\hat{R}}_{d}(m)} \right)^{- 1}{\hat{H}(m)}} = {\left( \begin{bmatrix}{R_{0,0}(m)} & {R_{0,1}(m)} & \ldots & {R_{0,{N_{r} - 1}}(m)} \\{R_{1,0}(m)} & {R_{1,1}(m)} & \; & \; \\\vdots & \; & \ddots & \; \\{R_{{N_{r} - 1},0}(m)} & \; & \; & {R_{{N_{r} - 1},{N_{r} - 1}}(m)}\end{bmatrix} \right)^{- 1}\begin{bmatrix}{{\hat{H}}_{0}(m)} \\{{\hat{H}}_{1}(m)} \\\; \\{{\hat{H}}_{N_{r} - 1}(m)}\end{bmatrix}}}$where {circumflex over (R)}_(d)(m) is an estimate of the covariancematrix of V(m). Using a Cholesky decomposition the covariance matrixbetween the antenna elements can be factored asL(m)·L ^(H)(m)={circumflex over (R)} _(d)(m)

The idea behind FDPE is to exploit this factorization and writeW _(MMSE)(m)=(L ^(H)(m))⁻¹((L(m))⁻¹ Ĥ(m))=W _(pre)(m)((L(m))⁻¹ H(m))so that the desired signal in the frequency domain becomes MMSEpre-equalized in the frequency domain, i.e. given byZ _(pre)(m)=W _(pre)(m)V(m).

This is a user independent processing, which is the same for all users.Hence the wideband received signal is transformed to the frequencydomain and the covariance matrix is computed and Cholesky factored,after which the whitened signal is computed. The signal is thentransformed back to the time domain where it is further processed foreach user. Note that the channels experienced by the RAKE receivers inthis processing are obtained from the second factor.

The FDE, Frequency Domain Equalization, algorithm performs equalizationand interference suppression in the frequency domain. Contrary to theFDPE, the FDE processing is performed individually for each user. Toexplain the FDE in, the following time domain signal model is used again

${v(t)} = {{\sum\limits_{l = 0}^{L - 1}\;{{h(l)}{z\left( {t - l} \right)}}} + {i(t)} + {{n^{thermal}(t)}.}}$

Here ν is the received (vector due to multiple antennas) signal, h isthe radio channel net response, z is the desired (transmitted) signal,i(t) is the interference and n^(thermal)(t) denotes thermal noise, tdenotes discrete time.

Taking the Fourier transform, translates the above equation intoV(m)=H(m)Z(m)+I(m)+N ^(thermal)(m)where the quantities are the discrete Fourier transform of thecorresponding time domain quantities. Now MMSE equalization can beperformed on V(m), separately for each user (different from the FDPEstructure). For this purpose, the channel is estimated using the pilotsignal, below this fact is emphasized by using the subscript_(u) foruser u. A first method to compute the MMSE filter for the FDE, usingtime domain calculations is described in E. Dahlman, S. Parkvall, J.Sköld and P. Beming, “3G Evolution—HSPA and LTE for mobilebroadband—section 5.1” 2:nd edition, Academic Press, 2008.

However, rather than computing the filter coefficients in the timedomain and then transforming to the frequency domain, the MMSE filtercoefficients can be directly computed as in T. Wigren, A. KAngas and H.Egnell, “Load estimation in frequency domain pre-equalization systems”,PCT/SE2010/051054.W _(u)(m)=H _(u) ^(H)(m)(H _(u) ^(H)(m)H _(u) ^(H)(m)+I _(u)(m)I _(u)^(H)(m)+(N ^(thermal)(m))^(H) N ^(thermal)(m))⁻¹ , u=1, . . . ,Uwhere the thermal noise power floor matrix estimate, can be obtained byany of the algorithms for noise floor estimation described above, andwhere H_(u)(m) is the sampled channel frequency response vector for useru. The use of frequency domain computation is less computationallycomplex than the method depicted in FIG. 1, and represents the preferredembodiment for implementation of the FDE.

Finally, the equalized signal is computed by a frequency domainmultiplication asZ _(FDE)(m)=W _(u)(m)V(m), u=1, . . . ,Uafter which the inverse FFT is applied to get the signal z_(FDE,u)(t).After this step processing proceeds as in a conventional WCDMA system.The processing is repeated for all users.

In the 3GPPUTRAN architecture, NBAP (Node B Application Part) is thesignaling protocol responsible for the control of the Node B by the RNC.RNSAP (Radio Network Subsystem Application Part) is a 3GPPsignalingprotocol responsible for communications between Radio NetworkControllers. The NBAP and RNSAP protocols allow for signaling ofReceived total wideband power (RTWF(t)), the estimated thermal noisefloor and the received scheduled enhanced uplink power (RSEPS(t)).

The details of the encoding of these messages appear in thespecifications 3GPP TS 25.433, UTRAN Ibu Interface Node B ApplicationPart (NBAP) Signaling and 3GPP TS 25.133, Requirements for support ofradio resource management.

The signaling breaks the estimated RoT into two pieces, the estimatednoise floor and the total wideband power. Note that 3GPP TS 25.433 and3GPP TS 25.133 state that it is the quantities at the antenna connectorthat are to be signaled, signaling of other related quantities in thesecontainers represents a proprietary solution.

U-TDOA (Uplink Time Difference of Arrival) is a real time positioningtechnology for wireless device networks that uses multilateration basedon timing of received uplink signals to locate the wireless device.

OTDOA (Observed Time Difference of Arrival) is another real timepositioning technology for wireless device networks that usesmultilateration based on timing of received downlink signals to locatethe wireless device.

The major conceptual difference between UTDOA and OTDOA is that theOTDOA requires multiple transmit points whilst UTDOA utilizes multiplereceive points at different locations (typically BS locations), althoughthe position calculation principle is the same.

FIG. 2 illustrates position calculation using the UTDOA method. Asillustrated there are three base stations 21 that measure timing ofreceived signals from a wireless device 22.

Assuming that the measurement are successful for the base stations 21,the following relations between the measured TOAs in the base stations21, the transmission time from the wireless device 22 and the distancesbetween the wireless device 22 and the base stations 21 follow:

$\quad\begin{matrix}{{t_{{TOA},1} + b_{clock}} = {T_{transmit} + {{{r_{1} - r_{Terminal}}}/c}}} \\\vdots \\{{t_{{TOA},n} + b_{clock}} = {T_{transmit} + {{{r_{n} - r_{Terminal}}}/{c.}}}}\end{matrix}$

Here t_(TOA,i), i=1, . . . , n denotes the measured time of arrivals(TOAs) in the known measuring locations r_(i), i=1, . . . , n,T_(transmit) denotes the transmission time from the wireless device 22and c is the speed of light. The boldface quantities are the (vector)locations of the base stations 21 and the wireless device 22. b_(clock)denotes the unknown clock bias of the wireless device 22 with respect tocellular system time. Now, in TDOA positioning, time of arrivaldifferences with respect to the own site are formed according to

$\quad\begin{matrix}{t_{{TDOA},2} = {{t_{{TOA},2} - t_{{TOA},2}} = {T_{transmit} - b_{clock} + {{{r_{2} - r_{Terminal}}}/c} - {{{r_{1} - r_{Terminal}}}/c}}}} \\\vdots \\{t_{{TDOA},n} = {{t_{{TOA},n} - t_{{TOA},1}} = {T_{transmit} - b_{clock} + {{{r_{n} - r_{Terminal}}}/c} - {{{r_{1} - r_{Terminal}}}/{c.}}}}}\end{matrix}$

In these n−1 equations, the left hand sides are known (with someadditional measurement error), provided that the time of transmissiondifference between the network and UE time can be measured. This isnormally achieved with dedicated hardware so called location measurementunits (LMUs) or by other procedures. In case of a synchronized networkthe difference is known. Further the locations of the base stations 21,r_(i), i=1, . . . , n, can be surveyed to within a few meters and sothey are known as well. What remains unknown is the wireless device 22location, i.e.r _(Terminal)(x _(Terminal) y _(Terminal) z _(Terminal))^(T).

In the more common case a two dimensional positioning is performed theunknown position is insteadr _(Terminal)=(x _(Terminal) y _(Terminal))^(T).

It then follows that at least three time of arrival differences areneeded in order to find a 3D wireless device position and that at leasttwo time of arrival differences are needed in order to find a 2Dwireless device position. This, in turn, means that at least four sitesneed to be detected for 3D wireless device positioning and at leastthree sites need to be detected for 2D wireless device positioning. Inpractice, accuracy can be improved if more measurements are collectedand a maximum likelihood solution is introduced. There may also bemultiple (false) solutions in cases where only a minimum number of sitesare detected. The UTDOA method belongs to the set of high precisionmethods, the inaccuracy is however significantly larger than that ofA-GPS. The main advantage of UTDOA is that it provides high precisionpositioning also indoors, a situation where the availability of A-GPS isvery limited.

To perform UTDOA timing measurements also on user data, to increase thesignal to noise ratio, one reference receiver de-codes the wirelessdevice signals, and forwards the sequence to cooperating receivers. Thisprocedure is relatively complex and requires a significant amount ofsignaling. The cooperating receivers are normally located in dedicatedhardware close to the positioning node. The decoded reference sequenceis used in order to regenerate the transmitted sequence from thewireless device, to allow correlation against each forwarded receivedset of data from the involved receivers in different locations(typically RBS locations).

The main problem with all terrestrial time difference of arrivalpositioning methods is to detect/be detected in a sufficient number ofnon-collocated locations. In the case of UTDOA the problem consists ofdetection of the same wireless device transmission in a sufficientnumber of WCDMA base stations (assuming that UTDOA timing measurementsare performed in connection to WCDMA RBSs). This is in general adifficult problem since it requires a sufficiently high signal to noiseratio in a number of locations sometimes far away from the wirelessdevice. It needs to be noted that the theoretical minimum of threeneighbor locations is not enough in practice. In many situations thenumber of neighbors may be twice this figure to obtain a reliableperformance.

There are however several problems with technology for UTDOA positioningknown in prior art.

In case several carriers are available in the base station, it is notknown in the positioning node which carrier, if any, UTDOA reference andreceivers are available for. Note that UTDOA radio measurements arenormally performed in separate HW, therefore it is not evident for whichcarriers this is possible. In general, having more carriers results in amore expensive radio system.

There is therefore a need for an improved solution for UTDOA positioningwhich solution solves or at least mitigates at least one of the abovementioned problems.

SUMMARY

An object of the present technology described is thus to provide amethod in a network node and a network node for UTDOA positioning whichsolves or at least mitigates at least one of the above mentionedproblems.

A first embodiment of the present technology described provides a methodin a network node with positioning functionality in a wirelesscommunications network in a multi-carrier system to enable UTDOA, UplinkTime Difference of Arrival, positioning measurements for a wirelessdevice in the multi-carrier system. The method comprising thesteps:receiving interference or load related information for carriersavailable for UTDOA positioning measurements; and selecting at least onecarrier for UTDOA positioning measurements based on the interference orload related information.

Thus, an object of the present technology described is achieved byreceiving interference or load related information for carriersavailable for UTDOA positioning measurements and selecting at least onecarrier for UTDOA positioning measurements based on the interference orload related information.

A second embodiment of the present technology described provides anetwork node with positioning functionality in a wireless communicationsnetwork in a multi-carrier system to enable UTDOA, Uplink TimeDifference of Arrival, positioning measurements for a wireless device inthe multi-carrier system. The network node being configured to receiveinterference or load related information for carriers available forUTDOA positioning measurements. The network node being furtherconfigured to select at least one carrier for UTDOA positioningmeasurements based on the interference or load related information.

An advantage of the present technology described is that it allows forselection of the most appropriate carrier to use for UTDOA positioningmeasurement.

Another advantage of the present technology described is that itimproves UTDOA positioning success probability, in particular in highuplink load.

Further advantages and features of embodiments of the present technologydescribed will become apparent when reading the following detaileddescription in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of the PoT estimation algorithm.

FIG. 2 illustrates schematically a principle for UTDOA positioncalculation.

FIG. 3 illustrates schematically an example network architecture of aRadio Access Network.

FIG. 4 illustrates a block diagram of the network node according to anexemplary embodiment of the present technology described.

FIG. 5 illustrates a flow diagram of a method according to an exemplaryembodiment of the technology described.

FIG. 6 illustrates a block diagram of the LTE positioning architecture

FIG. 7 illustrates a block diagram of the network node according to anexemplary embodiment of the present technology described.

DETAILED DESCRIPTION

In the following description, for purposes of explanation and notlimitation, specific details are set forth, such as particular sequencesof steps, signalling protocols and device configurations in order toprovide a thorough understanding of the present technology described. Itwill be apparent to one skilled in the art that the present technologydescribed may be carried out in other embodiments that depart from thesespecific details.

Moreover, those skilled in the art will appreciate that functions andmeans explained herein may be implemented using software functions inconjunction with a programmed microprocessor or general purposecomputer, and/or using an application specific integrated circuit(ASIC). It will also be appreciated that while the current technologydescribed is primarily described in the form of methods andarrangements, the technology described may also be embodied in acomputer program product as well as a system comprising a computerprocessor and a memory coupled to the processor, wherein the memory isencoded with one or more programs that may perform the functionsdisclosed herein.

FIG. 3 illustrates an example of a network architecture 30 where thenetwork node according to the present technology described may beimplemented. The wireless device 34 also denoted UE is used by asubscriber (not shown) to access services offered by an operator's corenetwork (CN) 33. The RAN 35 (Radio Access Network) is a part of thenetwork architecture 30 that is responsible for the radio transmissionand the control of radio connection. The RNS (Radio Network Subsystem)36 controls a number of BSs 32 in the RAN 35. The RNC 31 controls radioresources and radio connectivity within a set of cells (not shown). TheBS 32 handles the radio transmission and reception within one or morecells. A cell covers a geographical area. The Radio Link (not shown) isa representation of the communication between the wireless device 34 andone cell in the RAN 36. The lub interfaces 37 are connecting thedifferent BSs 32 to the RNCs in the RAN 35. The lur interfaces 38 areconnecting the different RNCs 31 in the RAN 35. User data is transportedon so-called transport bearers on these interfaces. Dependant on thetransport network used, these transport bearers could e.g. be mapped toAAL2 connections (in case of an ATM based transport network) or UDPconnections (in case of an IP based transport network).

The RAN 35 may redirect the wireless device 34 to another frequency. InUMTS, this is performed when the wireless device 34 is in CELL_FACHstate. When in the CELL_FACH state, the wireless device 34 autonomouslyselects carrier (not shown) (in 3GPP specifications, referred to as cellreselection) and signals the selected carrier according to a specified“cell update” procedure.

The carrier selection is essentially based on measurements of downlinksignal quality of the common pilot channel (CPICH), which is broadcastedin each cell with a constant transmit power. More specifically, thereare two options for quality metrics: Energy per chip divided by a totalreceived non-orthogonal interference power (Ec/NO) of the common pilotchannel (CPICH), or received signal code power (RSCP, i.e. signalstrength) of the CPICH. In prior art solutions there is thus no handovertriggered for the purpose UTDOA positioning measurements.

The 3GPP standardized two positioning architectures for control planepositioning. User plane UTDOA positioning is not possible since theUTDOA measurement is not available in the wireless device 34.

In the so-called RNC centric architecture the RNC 31 is the node wheremost positioning functionality is located. The RNC 31 receivespositioning requests from the CN 33, determines which positioning methodto use to serve the request, orders measurements to be performed by theBS 32 or the wireless device 34, computes the location of the wirelessdevice 34, and reports the result back to the CN 33.

In LTE the BSs denoted eNodeBs also perform certain position relatedmeasurements like the TA measurement. The wireless device may performcertain positioning-related measurements like the UE RxTx measurement.

The other architecture is the so called SAS (Stand alone Serving MobileLocation Centre) centric architecture. In this architecture most ofpositioning functionality is taken over by the broken out SAS node,leaving the RNC as a measurement and positioning reporting relay node.

Further, three key network elements in the 3GPP positioning architectureare the LCS (Location Services) Client, the LCS target and the LCSServer. The LCS Server is a physical or logical entity managingpositioning for a LCS target device by collecting measurements and otherlocation information, assisting the LCS target in measurements whennecessary, and estimating the LCS target location. A LCS Client is asoftware and/or hardware entity that interacts with a LCS Server for thepurpose of obtaining location information for one or more LCS targets,i.e. the wireless device being positioned. LCS Clients may reside in theLCS targets themselves, radio node (e.g., eNodeB in LTE), core networknode, PSAP (Public Safety Answering Point), etc. An LCS Client sends arequest to LCS Server to obtain location information, and LCS Serverprocesses and serves the received requests and sends the positioningresult and optionally a velocity estimate to the LCS Client. Apositioning request can be originated from the wireless device, radionetwork or core network. Position calculation for UTDOA would betypically conducted in the network (e.g., positioning node which isE-SMLC or SLP in LTE) or by an external node.

Below is as an example of the positioning architecture more specific toLTE described. LPPa is a protocol between eNodeB and LCS Server, usedfor control-plane positioning procedures, assisting user-planepositioning by querying eNodeBs for information and eNodeB measurements,to be enhanced also to support UL positioning. SUPL protocol may be usedas a transport for LPP in the user plane. In the user plane with SUPL, aUE is typically referred to as SUPL Enabled Terminal (SET), the LCSplatform is typically referred to as SUPL Location Platform (SLP).LCS-AP protocol is between MME and E-SMLC. Positioning is typicallytriggered via LCS-AP by MME itself or upon request from other nodes(e.g., eNodeB, PSAP, etc.) or UE.

A schematic block diagram of the architecture defined in the currentstandard is illustrated in FIG. 6 focusing on UL positioning support,where the LCS target is a wireless device 63, and the LCS Server is anE-SMLC 61 or an SLP 62. In the FIG. 6, the control plane positioningprotocols 64 with E-SMLC as the terminating point are shown. The userplane positioning protocol 65 is also shown. SLP 62 may comprise twocomponents, SPC and SLC (not shown), which may also reside in differentnodes (not shown). In an example implementation, SPC has a proprietaryinterface with E-SMLC, and Llp interface with SLC, and the SLC part ofSLP 62 communicates with P-GW (PDN-Gateway) and External LCS Client 66.

To support UTDOA in LTE, also UTDOA-specific protocols are beingintroduced in 3GPP. Thus, the SLm interface 67, between the E-SMLC 61and LMU 68 is used for uplink positioning. The interface is terminatedbetween a positioning server (E-SMLC 61) and LMU 68. It is used totransport LMUP protocol messages (not shown) over the E-SMLC-to-LMUinterface 67. There are three different deployment options with LMU 68.As show in the FIG. 6, an LMU 68 may be integrated into eNodeB, sharesome equipment such as antenna with eNodeB, or be a standalone physicalnode with own antenna. An LMU 68 may be associated with one or morecells or radio BSs, so there may be scenarios where an LMU 68 couldbenefit or even has to support (in case of no continuous coverage on onefrequency) more than one frequency. Further, one could also envisionthat an LMU 68 supports a set of frequencies (e.g., the LMU capabilityrelated to multi-frequency support) which is different from thatsupported by an eNodeB to which the LMU 68 may be associated. Further,in the technology described, the carrier capability may relate tosupported frequencies, but also the combinations of and the maximumnumber of simultaneously measured frequencies.

As mention above, the technology described discloses methods andarrangements for selection of the most appropriate carrier to use forUTDOA positioning measurement. One important criterion that needs to bemet for a successful UTDOA positioning is successful detection anddecoding in the UTDOA reference measurement location. Another importantcriterion is successful detection in as many UTDOA neighbor measurementlocations as possible. Both criteria are associated with the uplinkinterference situation or load situation. This is one reason why thenetwork node according to the present technology described is configuredto receive interference or load related information in order to assessthe interference situation or load situation on different carriers. Inexemplary embodiments, as will be described, the network node is furtherconfigured to receive a capability indicator that states among othersfor which carriers frequencies UTDOA positioning measurements can bedone.

FIG. 4 is a schematic block diagram illustrating a network node 40 withpositioning functionality according to an exemplary embodiment of thepresent technology described. The network node 40 being configured toreceive interference or load related information for carriers availablefor UTDOA positioning measurements. The network node 40 being furtherconfigured to select at least one carrier for UTDOA positioningmeasurements based on the interference or load related information.

In embodiments of the technology described the network node 40 may beany radio node transmitting radio signals that may be used forpositioning measurements, e.g., NodeB, eNodeB, location measurement unit(LMU) (e.g., UTDOA measurement devices are normally mounted at Node Bs),macro/micro/pico base station, home NodeB, relay, remote radio heads,sensor, multi-RAT or multi-standard radio base station, or repeater. Thenetwork node 40 may also be a RNC or a SAS.

The interference related information that is received by the networknode 40 may comprise any one or more of: RoT, Rise over Thermal, ornoise rise, own cell interference, neighbor cell interference, thermalnoise power or total wideband power. In case of a RNC centricarchitecture, where an RNC (not shown) is the network node 40 theinterference related information can be signalled over the lub interfacebetween the base station (not shown) and the RNC. The network node 40 isconfigured to receive the interference or load related information, overan internal interface (not shown), in case the network node 40 not beingin the RNC. However, where the network node 40 is for instance a SASnode, the network node 40 is configured to receive the interference orload related information over a lupc interface (not shown) to thenetwork node 40.

The load related information in embodiments of the present technologydescribed may be the load on the air interface and thus the signalquality for carriers available for UTDOA positioning measurements.Further the load related information may include measured bandwidth onthe carriers available for UTDOA positioning measurements. Otherinformation that the load related information may be is frequency sincelower frequencies typically provide better coverage which is crucial inlarge cells and may be not necessary in small cells. The load relatedinformation may also be provided for a specified frequency. The loadrelated information may also comprise at least one value or descriptorrepresenting the load situation or number of scheduled wireless devicesor Rot over air interface for cells and carriers available for UTDOApositioning measurements.

The selection of the at least one carrier that the network node 40 isconfigured to perform based on the interference or load relatedinformation may be computed using different algorithms. In an exemplaryembodiment the network node 40 may be further configured to select theat least one carrier for UTDOA positioning measurements based on networkresource optimization since the resources for positioning measurementsare shared with other services.

In order to improve the use of more than one carrier in UTDOApositioning, information about carrier capability and multi-carriercapability may be necessary in the network node 40. Further, thisinformation enables configuring transmissions optimized for UTDOAmeasurements. Therefore in yet another exemplary embodiment of thepresent technology described the network node 40 is further configuredto receive at least one capability indicator that states for whichcarrier frequencies UTDOA positioning measurements can be done. In thisexemplary embodiment the network node 40 is yet further configured toselect the at least one carrier based on the at least one capabilityindicator. The at least one capability indicator may be received fromthe wireless device, a radio node or another node. The capabilityindicator may also comprise information about carrier frequenciessupported for UTDOA measurements, wireless device multi-carriercapability or radio node multi-carrier capability.

According to exemplary embodiments of the technology described, thenetwork node 40 is aware of the carrier capability of the radio nodesthat may be involved in UTDOA measurements. The capability indicator maycomprise information about frequencies supported for UTDOA measurements.In one embodiment, the capability indicator may include frequency bandinformation and/or duplex mode (e.g., half-duplex) and/or carrierbandwidth available for UTDOA measurements.

In yet another exemplary embodiment the capability indicator may includefrequency capability information, e.g., a binary indicator or the numberof frequencies available for multi-carrier operation which may e.g. be2, 4 or 8. The capability indicator may further include an indicationwhether the multi-carrier operation is supported and/or configured byradio nodes that may be involved in UTDOA measurements. In anotherexemplary embodiment of the network node 40, the capability indicatorfurther comprises information related to any one or a combination offrequency band: duplex mode and/or carrier bandwidth available for UTDOAmeasurements, supported by wireless device or the radio node involved inUTDOA measurements.

As mention above multi-carrier capable wireless devices may transmit thesignal over multiple carriers, radio nodes that may be involved in UTDOAmeasurements need to be aware of this. It is also an advantage if thenetwork node 40 is aware of this. In an exemplary embodiment of thenetwork node 40 this information may be comprised in the capabilityindicator. For instance all carriers supported by the wireless devicemay be available for UTDOA measurements, but this is not always thecase. Further, since the wireless device and the radio node involved inUTDOA measurements may support different number and, the capabilityindicator may include the number or the combination of frequenciesavailable for multi-carrier operation. For example, there may bedual-carrier wireless devices in multi-carrier system which maygenerally support up to e.g. 4 or 8 carriers.

In yet another embodiment of the network node 40, the capabilityindicator may also be exchanged between radio nodes involved in UTDOAmeasurements, e.g., location measurement units (LMU) and NodeB orbetween LMUs or between NodeBs over the corresponding interfaces. Inanother embodiment of the network node 40, the capability indicator maybe obtained (upon a request or without it) from another node, e.g., O&Mor SON. In still another embodiment the network node 40 may inform thewireless device or the radio node scheduling the wireless device on thepreferred/possible frequencies on which to transmit for UTDOApositioning, thereby reflecting the capability indicator.

In another exemplary embodiment of the network node 40 according to thetechnology described the network node 40 is further configured toconfigure UTDOA measurements in at least one radio node involved inUTDOA measurements on the selected carrier for UTDOA positioningmeasurements. In this embodiment the network node 40 may be furtherconfigured to configuring selection, reselection or switching of thecarrier for performing UTDOA measurements, based on the interference orload related information or capability indicator. In yet anotherexemplary embodiment the network node 40 triggers a switch to theselected carrier for the wireless device.

In another exemplary embodiment of the network node 40 the network node40 is further configured to switch the primary carrier for the wirelessdevice supporting multi-carrier operation or configure simultaneoustransmissions on carriers, where the set of carriers configured forUTDOA may be smaller than the set of carriers supported in the network,depending e.g. on the capability indicator. The network node 40 may alsobe further configured to change from/to single-carrier operation forUTODA in the network supporting more than 1 carrier in general. Inanother embodiment, the network node 40 accounts for the wireless devicefrequency capability, for UTDOA when selecting preferable frequencies.In yet another embodiment, wireless device frequency capabilitystatistics is collected in the network node 40. In this exemplaryembodiment the selection of the preferred carrier may be based also onthis statistics.

The network node 40 may also receive per carrier such information as thenumber of scheduled wireless devices, number of voice wireless devices,or any information reflecting the number of CS users and the totalnumber of wireless devices, etc.

FIG. 7 is a schematic block diagram illustrating another exemplaryembodiment of the network node 40. In this embodiment the network node40 comprises receiving means 71 configured to receive interference orload related information for carriers available for UTDOA positioningmeasurements. The receiving means 71 is configured to receive same typeof interference related information and load related information as inthe previously described embodiments of the network node 40. Thereceiving means is configured to receive interference or load relatedinformation over the interfaces (not shown) described in the previouslyembodiments. In this embodiment the network node 40 further comprisesprocessing means 72, connected to the receiving means 71, configured toselect at least one carrier for UTDOA positioning measurements based onthe interference or load related information as described in theembodiments above.

The receiving means 71 is in yet another embodiments further configuredto receive at least one capability indicator that states for whichcarrier frequencies UTDOA positioning measurements can be done. Thecapability indicator comprises at least the same type of information asthe previously described embodiments of the network node 40. In thisexemplary embodiment the processing means 72 is yet further configuredto select the at least one carrier based on the at least one capabilityindicator. The processing means 72 is further configured in yet anotherembodiment to triggers a switch to the selected carrier for the wirelessdevice and/or to switch the primary carrier for the wireless devicesupporting multi-carrier operation in accordance with previouslydescribed embodiments.

Radio nodes involved in UTDOA measurements according to the presenttechnology described may apply interference suppressing receivers in theradio nodes in order to enhance the receiver performance. In that casethe effective load is reduced. Instead of IS, interference cancellationmay also be used and the load related information after applyinginterference cancellation may also be received by the network node 40.

Another aspects of the present technology described relates methods formeasurement of the load in terms of RoT, accounting for IS gains. TheRoTis given from

${{{RoT}_{u}^{G +} \equiv \frac{S_{u}^{G +} + I_{u}^{G +} + {\kappa_{u}^{G +}\hat{N}}}{\kappa_{u}^{G +}\hat{N}}} = {\frac{S_{u}^{G +}}{\kappa_{u}^{G +}\hat{N}}\left( {1 + {\frac{{SF}_{u,{EDPCCH}}}{\beta_{u,{Effective}}^{2}}\frac{1}{{SINR}_{u}^{G +}}}} \right)}},{u = 1},\ldots\mspace{14mu},{{U.\kappa_{u}^{G +}} = {\left( {\hat{w}}_{u} \right)^{H}{\hat{w}}_{u}}},\mspace{14mu}{u = 1},\ldots\mspace{14mu},{{U.{RoT}^{G +}} = {\max\limits_{u}{{RoT}_{u}^{G +}.}}}$

Here RoT_(u) ^(G+) is the load seen by user u, S_(u) ^(G+) is the powerof user u measured after the G-rake, SF_(u,EDPCCH) is the spreadingfactor, β_(u,effective) is the total power factor, and S/NR_(u) ^(G+) isthe signal to interference ration measured after G-rake, i.e. thequantity that closes the inner power control loop. As can be seen, thecell load is selected as the maximum rise over thermal, as seen by anyuser of the cell. This is the limiting user of the cell.

An equivalent of the RoT can be computed after FDPE IS gains. The endresult is given by

${RoT}^{FDPE} = {\frac{{z_{pre}^{H}(t)}{z_{pre}(t)}}{\left( {\sum\limits_{l = 0}^{L - 1}\;{{w_{pre}^{H}(l)}{w_{pre}(l)}}} \right)\left( {\sum\limits_{a = 1}^{A}\;{\hat{N}}_{a}^{thermal}} \right)}.}$

Here RoT^(FDPE) is the load, z_(pre)(t) is the whitened signal in thetime domain, w_(pre)(l), l=0, . . . , L−1 is the impulse response of thewhitening filter, and {circumflex over (N)}_(a) ^(thermal), a=1, . . . ,A, are the estimated thermal noise floors of the A antenna branches.

The quantities above should be computed as averages or estimates over atime interval where the whitening filter of the FDPE remains constant.Since the total received wideband power is summed over all antennabranches, so is the thermal noise power floor. The RoT after FDPE isalso scaled with the power of the pre-whitening filter. It can be notedthat the use of FDPE handles the received signal as a whole, without aneed to consider individual users. This advantage is retained for theload estimation algorithm.

An equivalent of the RoT can be computed after FDE IS gains, for eachuser. The end result is given by,

${{RoT}_{u}^{FDE} = \frac{{z_{{FDE},u}^{H}(t)}{z_{{FDE},u}(t)}}{\left( {\sum\limits_{l = 0}^{L - 1}\;{{w_{u}^{H}(l)}{w_{u}(l)}}} \right)\left( {\sum\limits_{a = 1}^{A}\;{\hat{N}}_{a}^{thermal}} \right)}},\mspace{20mu}{u = 1},\ldots\mspace{14mu},{U.}$

Here RoT_(u) ^(FDE) is the load of user u, z_(pre,u)(t) is the whitenedsignal in the time domain, w_(pre,u)(l), l=0, . . . , L−1 is the impulseresponse of the whitening filter, and {circumflex over (N)}_(a)^(thermal), a=1, . . . , A, are the estimated thermal noise floors ofthe A antenna branches.

The quantities above should be computed as averages or estimates over atime interval where the equalizing filter of the FDE remains constant.Since the total received wideband power is summed over all antennabranches, so is the thermal noise power floor. The RoT after FDE is alsoscaled with the power of the equalizing filter. As in the G-rake case,the dominating user of the cell is selected as

${RoT}^{FDE} = {\max\limits_{u}{RoT}_{u}^{FDE}}$

The RoT before and/or after IS processing normally varies fast, beingaffected e.g. by channel variations. The carrier selection according tothe present technology described is a slower selection process ascompared to the variations in RoT. Therefore, exemplary embodiments ofthe network node therefore rather rely on interference or load relatedinformation based on the average uplink load, obtained for a typicaltime interval. This time interval or filtering time constant ispreferably tuned to be of the same order as the bandwidth of the carrierselection process.

As a typical embodiment of this filtering process a first orderautoregressive filter can be used:

RoT

(t+T)=α

RoT

(t)+(1−α)RoT_(Input)(t)where

RoT

is the average load, T is the update time period, e.g., 10 ms, α is thetime constant and RoT_(Input) is any of the RoT at the antennaconnector, RoT^(G+), RoT^(FDPE) or RoT^(FDE).

This filtering is preferably performed in the network node 40 accordingto the present technology described.

The RoT after IS processing have no associated signalling—the definitionof the measurement of these RoT equivalents are different from the airinterface RoT.

As mentioned above, the network node 40 is therefore in an exemplaryembodiment configured to select the carriers for which RoT of variouskinds shall be measured. Note that the measurements are however notlimited to only RoT.

In exemplary embodiments the selection is further based on the receivedcapability indicator containing e.g. information about UTDOA positionmeasurement capability. In another exemplary embodiment is the selectionalso based on the database of cell relations, cell positions and antennadirections that needs to be configured in the network node, or at leastbe available in the network node.

In yet another embodiment the network node 40 is further configured toindicate a measurement order and information of which type of RoT thatis preferred.

The interference related information that is received by the networknode 40 may comprise RoT measurement information, together with anindication of what type of RoT information that is signalled.

In an exemplary embodiment the network node 40 is configured to evaluatea criterion, for each carrier alternative, where the criterion isresponsive to the measured and received load related information, i.e.

RoT

(carrier,cell), cell ε{cell_(i)}, iε{neigbors}carrier ε{UTDOA capablecarriers}. This is however not enough. The neighbour cells havedifferent antenna directions and locations as well. Therefore the loadrelated informationmay be complemented with the predicted path loss andthe predicted antenna gain, for each cell. This information needs to beavailable in databases, accessible by the network node 40.

It is now possible to set up a cost for each cell and carriercombination,J(carrier,cell,servingcell)=

RoT

(carrier,cell)+

Pathloss

(carrier,cell,servingcell)|−

Antennagain

(cell,servingcell)

Here the path loss is counted from the centre of the serving cell to theantenna location of the RBS of the associated UTDOA location measurementunit. The antenna gain is computed using the angle between the centre ofthe serving cell and the antenna location of the RBS of the UTDOAposition measurement unit.

The bore sight angle of the antenna of the cell of the RBS of the UTDOAposition measurement unit.

All quantities are expressed in dB. The network node 40 then selects thecarrier by calculation of

The minimum threshold value J(carrier), for each carrier, for whichJ(carrier,cell,servingcell)≦ J(carrier) for N cells, and

${selectedcarrier} = {\underset{carrier}{argmin}{\overset{\_}{J}({carrier})}}$

The network node 40 is as described above in an exemplary embodimentconfigured to force the wireless device to the selected carrier, both incase of conventional carrier selection performed by the RNC and multicarrier. The network node 40 may be configured to trigger or initiatehandover and carriers switching. In UMTS, these decisions are typicallymade by the RNC and possibly the NodeB. In the prior art, however, thesedecisions cannot be triggered by UTDOA positioning functionalityaccounting to optimize UTDOA performance.

Referring to FIG. 5 there is illustrated a flowchart of a methoddescribing the steps in the network node 40 with positioningfunctionality in a wireless communications network in a multi-carriersystem to enable UTDOA, positioning measurements for a wireless devicein the multi-carrier system, in accordance with previously describedembodiments of the present technology described. As shown in FIG. 6, themethod comprises:

500 receiving interference or load related information for carriersavailable for UTDOA positioning measurements; and

510 selecting at least one carrier for UTDOA positioning measurementsbased on the interference or load related information.

As previously described the method may also comprise the further step of(not shown) configuring UTDOA measurements in at least one radio nodeinvolved in UTDOA measurements on the selected carrier for UTDOApositioning measurements. This step may also comprise selection,reselection or switching of the carrier for performing UTDOAmeasurements, based on said interference or load related information orcapability indicator.

In another embodiment of the method, the method comprising a furtherstep of, prior to the step of receiving, receiving also at least onecapability indicator that states for which carriers frequencies UTDOApositioning measurements can be done. In this embodiment the step ofselecting is further based on the at least one capability indicator.

In yet another exemplary embodiment of the method, the method comprisesa further step of, after the step of selecting, configuring transmissionfor the wireless device on the selected carrier for UTDOA positioningmeasurements.

Although this description is mainly given using the term wirelessdevice, it should be understood by the skilled in the art that wirelessdevice is a non-limiting term which means any UE, User Equipment, ornode (e.g. PDA, laptop, mobile, sensor, fixed relay, mobile relay oreven a small base station that is being positioned when timingmeasurements for positioning are considered, i.e. a LCS target ingeneral). The technology described applies both for wireless devicescapable and not capable of multi-carrier operation.

The embodiments are not limited to WCDMA, but may, with obviousmodifications, apply with any RAN, single- or multi-RAT. Some other RATexamples are LTE, LTE-Advanced, UMTS TDD, GSM, cdma2000, WiMAX, andWiFi. A multi-carrier network node may be also the network node capableof carrier aggregation for UMTS and LTE, which in addition may also be amulti-standard radio base station.

The invention claimed is:
 1. A method in a network node with positioningfunctionality in a wireless communications network in a multi-carriersystem with carrier aggregation, each aggregated carrier correspondingto a component carrier, to enable positioning measurements for awireless device in the multi-carrier system, the method comprising thesteps: obtaining a multi-carrier capability of a radio node capable ofperforming positioning measurements, receiving at least one capabilityindicator that identifies on which carrier frequencies positioningmeasurements can be done; and selecting at least one of the multiplecarrier frequencies for positioning measurements on radio signalstransmitted by the wireless device based on said at least one capabilityindicator.
 2. The method of claim 1, further comprising a step of, aftersaid step of selecting, configuring positioning measurements in at leastone radio node on said selected carrier frequency for positioningmeasurements.
 3. The method of claim 2, wherein the radio node is anyof: an eNodeB, NodeS, or location measurement unit (LMU).
 4. The methodof claim 1, wherein the step of configuring is further comprisingselection, reselection, or switching of the carrier frequency forperforming positioning measurements.
 5. The method of claim 1, whereinsaid step of receiving at least one capability indicator furthercomprises receiving the at least one capability indicator from a userequipment (UE), a radio node, or another network node.
 6. The method ofclaim 1, wherein the capability indicator further comprises at least oneof: information about carrier frequencies supported for positioningmeasurements, a user equipment (UE) multi-carrier capability, or radionode multi-carrier capability.
 7. The method of claim 1, wherein thecapability indicator further comprises information related to any one ora combination of: frequency band, duplex mode, and/or carrier frequencybandwidth available for positioning measurements supported by a userequipment (UE) or at least one radio node on said selected carrierfrequency.
 8. The method of claim 1, wherein the network node is any of:a positioning node, radio network controller, evolved-serving mobilelocation center (E-SMLC), Stand alone Serving Mobile Location Centre(SAS), location measurement unit (LMU), or eNodeB.
 9. The method ofclaim 1, wherein the capability indicator further comprises any one ormore of: an indication of whether multi-carrier operation is supportedand/or configured by at least one radio node on said selected carrierfrequency, a number of carrier frequencies that can be configured formulti-carrier operation, or a combination of carrier frequencies that isconfigured for multi-carrier operation or that is relevant forpositioning measurement.
 10. The method of claim 1, wherein thecapability indicator further comprises the information about whichcombinations of two or more carrier frequencies are supported by a userequipment (UE), configured for the UE, or available for positioningmeasurements.
 11. The method of claim 1, wherein said method comprisinga further step of, after said step of selecting, configuringtransmission for said wireless device on said selected carrier frequencyfor positioning measurements.
 12. The method of claim 11, wherein saidstep of configuring further comprises carrier frequency switching orhandover for said wireless device.
 13. A network node with positioningfunctionality in a wireless communications network in a multi-carriersystem to enable positioning measurements for a wireless device in themulti-carrier system, the network node comprising: communicationscircuitry configured to receive at least one capability indicator thatidentifies on which carrier frequencies positioning measurements in themulti-carrier system can be performed; and one or more data processorsconfigured to obtain a multi-carrier capability of a radio node toperform positioning measurements and to select at least one of themultiple carrier frequencies for positioning measurements on radiosignals transmitted by the wireless device based on said at least onecapability indicator.
 14. The network node of claim 13, wherein thenetwork node is configured to configure positioning measurements in atleast one radio node on said selected carrier frequency for positioningmeasurements.
 15. The network node of claim 14, wherein the radio nodeis any of: an eNodeB, NodeS, or location measurement unit (LMU).
 16. Thenetwork node of claim 13, wherein the network node is configured forselection, reselection, or switching of the carrier frequency forperforming positioning measurements.
 17. The network node of claim 16,wherein said at least one capability indicator is received from a userequipment (UE) a radio node, or another network node.
 18. The networknode of claim 13, wherein the capability indicator further comprises atleast one of: information about carrier frequencies supported forpositioning measurements, user equipment (UE) multi-carrier capability,or radio node multi-carrier capability.
 19. The network node of claim13, wherein the capability indicator further comprises informationrelated to any one frequency band or a combination of frequency bands:duplex mode and/or carrier frequency bandwidth available for positioningmeasurements supported by the wireless device or the radio node.
 20. Thenetwork node of claim 13, wherein the radio node is any of: apositioning node, radio network controller (RNC), evolved-serving mobilelocation center (E-SMLC), Stand alone Serving Mobile Location Centre(SAS), location measurement unit (LMU), or eNodeB.
 21. The network nodeof claim 13, wherein the capability indicator further comprises any oneor more of: an indication on whether multi-carrier operation issupported and/or configured by the radio node, number of carriers thatcan be configured for multi-carrier operation, combination of carriersconfigured for multi-carrier operation or relevant for positioningmeasurements.
 22. The network node of claim 13, wherein the capabilityindicator further comprises the information about which combinations oftwo or more carrier frequencies are supported by a user equipment (UE),configured for the UE, or available for measurements.
 23. The networknode of claim 13, wherein said network node is configured to configuretransmission for said wireless device on said selected carrier frequencyfor positioning measurements.
 24. The network node of claim 23, whereinsaid network node is configured to perform carrier frequency switchingor handover for said wireless device.